Fluidized carbonization process



Patented Jan. 15, 1952 zsaznn rwmrzrn caanomzarron raocrss Karl J. Nelson, Craniord, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application Ma 11, 1947, Serial No. 748,796

9 Claims. 1

The present invention relates tothe handling of carbonaceous solids.- More particularly, the

invention is concerned with the treatment of finely divided carbonaceous solids such as all types of coal, brown coal, lignite, oil shale, tar sands, asphalt, cellulosic materials including iignin, etc. to produce valuable volatile products.

Heretofore, solid carbonaceous materials of the type mentioned above have been treated at elevated temperatures in fixed bed operation to form liquid and gaseous fuels such as light oils, tars, coal gas, producer gas and water gas. However, these processes involve either discontinuous operation'or ineflicient conversion of the available carbonaceous matter into volatile fuels and heat.

The operation of these processes may be made iully continuous by employing the so-called fluid solids technique in which the reactions take place in dense fluidized beds of finely divided solids maintained in a turbulent ebullient state by means of fluidizing gases. This technique has highly desirable additional advantages including greatly improved heat distribution and ease of solids handling.

However, serious difllculties have been encountered in handling the finely divided raw material. It is well knownthat most coals below the rank of anthraciteand above that of lignite as well as certain types of low temperature coke, shales, etc., undergo some degree of softening when heated. Such materials do not have sharply defined softening points. There is, however, a characteristic temperature range for each coal in which softening will occur. At this temperature range liquid products are formed which may be suflicient to cause the whole mass of coal to coagulate more or less completely. The degree of softening, or melting varies widely for different coals from only a slight agglomeration of individual particles to a melting so complete that the coal liquefies and all traces of individual particles disappear.

The processing of coals and similar materials exhibiting any appreciable degree of fusion, for example in carbonization, gasification, producer gas operation, etc., is extremely diflicult because fusion leads to excessive plugging of the equipment and it contributes to channeling of reactants, as'well as appreciable increases in pressure drop through the system; These objections are particularly critical in processes employing the fluid solids technique, which depend on intimate and complete rapid mixing in a turbulent bed of fluidized solids. If any appreciable amount of fusion occurs in the fluid bed, the fluid properties of the bed are lost and the process becomes inoperable.

It has been demonstrated in the fluid proc essing of plasticizing type carbonaceous solids that operable conditions can be maintained if each particle of fresh coal is completely surrounded and i imately mixed with dry" processed mate al, that is, non-plasticizing coke. In its in e specific aspects, the present invention mat; to an improvement of this type of process by which agglomeration, or plugging of the plasticizing carbonaceous solids charge may be completely eliminated in an economical manner.

In accordance with the present invention, plasticizing carbonaceous solids of fluidizable particle size are charged to a mixing and preheating zone which is surrounded by and in open communication with the relatively dense fluidized mass of carbonaceous solids being processed in a large processing zone at a processing temperature above the piasticization temperature of the charge, while simultaneously causing hot processed solids from said surrounding fluidized mass to enter said mixingzone and to to an intimate mixture with the fresh charge. Gases required for processing and/or heating the charge are passed upwardly through the inner mixing and preheating zone in such a manner as to force "dry processed solids substantially at processing temperature from said surrounding fluidized mass into said mixing zone through its lower opening and to discharge a mixture of fresh and dry material preheated to processing temperature from the upper opening of the mixing zone into said surrounding fluidized mass. -The inner mixing zone is operated at relatively high velocities, of the order of 3-30 feet per second, so. that the time of residence of solids passing from the bottom to the top of this zone averages from about 3 to seconds. Thus, onl suilicient time is allowed in this zone to raise the temperature of the fresh charge to reaction temperature which is normally appreciably above the fusion temperature. This heating takes place under conditions at which each particle of fresh charge is completely surrounded by dry" coke.

The major portion of the gases from the high velocity zone disengage from the solids at the top of the surrounding fiuid bed. However, a small portion of such gas is occluded by the solids which enter, and flow down through, the

annular space formed by the walls of the larger processing zone and theinner mixing and preheating zone.

together with the volatile products formed in the annular space is normally sufllcient to maintain a freefiowing solids mass 'ofa high density in the annular zone, so as of coke of the order of- -50 times-the weight of I incoming fresh charge, tothe lower opening on- It may and ,through,;:the inner mixing zone. also be desirable to inject into the annular space additional fluidizi'ng gas to improve flow conditions.

itself equally well to the carbonization of carbonizable solids and to-the gasification of carbonaceous solids with oxidizing-gases as will become more readily apparent from the following more detailed description read with reference to l the accompanying drawing wherein: Figure 1 is a partly schematic partly diagrammatic view of a system suitable for the carboniization of 'coal or the like in'accordancewlth the invention; and 1 Figure 2 is a similar view of a system adapted. for the production of volatile fuels free from flue.

to provide an adequate pressure diilerentialbetween the annular; and inner zones to assure high circulation rates Figure -1 of the drawing, the

The functions and 00013615.,

This amount of entrained gas The process of the present invention lends to, and preferably directly into, the 1owe r end of mixing chamber 30. I 1

The amount of oxidizing gas supplied to mixin chamber 30 is so controlled that any heat required in additionto the gas preheat, to maintain' the coal in chamber at a carbonization temperature of about 900'-1400 F., is generated within'imixingchamber by a controlled com- .,'bustion;"of' combustibleicoal constituents and that 10, f consumed; by the.i;.t ime,,the gas reaches the top of chamber'ali soajstoprevent volatile product comthe oxygen i supplied'is substantially completely bustioninchamb'er and section 25. The gas mixture supplied bypipe l5 enters mixing chamber 30 at a superficial velocity high enough to form a fluidized,,vio1ently' turbulent, upfiowing solidsphase therein 'offrelatively low apparent density. ';-'Hot char'of carbonization temperature in amounts greatly exceeding the amount of i got mixing ch after in connection with the carbonization crviously mentioned may be processed for the same.

or different purposes in a generally .analogous manner.

In operation, the annular space 22 formedbyl,

, I addition of fiuidizing gas through taps 40.

the walls of processing chamber 20 and mixing 1 chamber 30 is filledwith' a dense, free-flowing;v

fluidized mass of finely divided coal undergoing carbonization as will appear more clearly hereinafter. Fresh finely divided bituminous coal is supplied through feed line" 'I' to the lower portion of mixing chamber 30. The coal may have'a particle size of about 8 mesh or by zero although particle sizes from smaller thanv 400;m esh to as large as /2" in diameter may be used.

Feed line I may be a section of any conventional means for conveying finely divided solids,

such as an aerated standpipe, a screw conveyor,

a starfeeder or the like.' However, a feed mechanism as illustrated by the drawing is preferred for most economical operation, When'using a mechanism of this type, the coal issupplied to a revolving feed hopper; I which discharges coal," on a revolvingtable feeder 3 cooperating-with a; knife 4 to feed'thefcoal to a compressive, screw conveyor 5'which transportsthe coal to the lower I portion of mixing chamber 30. This'feeding'arrangement is particularly suitable for handling coals having sticky characteristics which may be due to high moisture content of the coals.

An oxidizing gas, such as air and/or oxygen} 11 preferably preheated, which may be diluted with superheated steam and/orproduct gas or the like supplied by blower 9 is fed, if desired, over a knockout drum 1 I, through line l3 to gas feed pipe l5 arranged in the bottom portion of chamber 20. Gas feed pipe l5 should discharge close freshchargesupplied, is forced under the pseudohydrostatic pu essure of the relatively dense solids phase-in annulars'pace into the lower... open: mberfillwhere itis picked up' 'es and thoroughly mixed with aslto envelopeachparticle of assess-erases plasticiz'ing/ coal :"with non-plasticizing V dryf' char of carbonizatio'n temperature. Inthis manner, the adverse effects, of coal plasticization are completely eliminated while the fresh charge is rapidly heated beyond plasticization temperature and up'to carbonization temperature at which it is maintained in space22 for a time sufficient to complete carbonization. The proportion of char supplied from annular space 22 to chamber 311 may be readily-controlledby'the superficial velocity. of the gasesjin' chamber 30, determining the pressure differential between annular space 22 and chamber 30. addition this pressure dif-, ferential may be modified, by varying the density of the fluidized mass inzone 22 by the controlled The relatively-dilute; fluidized suspension of char and fresh coal discharges at carbonization temperature from the top. of chamber 30 into the larger diameter space of chamber 20. As a result of the decrease in superficial gas velocity,

a major portion ofthe solids separates from the gas to enter annular space 22 and to repeat the cycle. This separation effect may be enhanced by providing chamber "with a top' 'section 25 of enlarged diameter'so that chamber 20. will be filled with adense fluidized solids phase having awell defined level'Li Normally, sufllcient gas is occluded by'the separating solids to maintain. together. with the volatile products formed in annularv space 22, the solids in this annular space in a free flowing fluidized form. However, small amounts of, additional fluidizing gas, such as qsteam, inert gas product gas, air, etc., may be upplied fthrough manifold 21, 28 to the bottom 1'" nnularspace 22fand/or through taps 40 to improve iiuidization, or modifytheapparent den- 'sit y-if desired. I

The conditions of gas-flow, oxygen supply, coal feed and char recycle rates may vary .widely depending on the carbonization temperature desired and the character oi the fresh coal. Quite generally, it may be stated that for the more common bituminous carbonization coals, the system may be successfully operated at fresh feed temperaturesv of-about 60-600 F., carbonizatlon and char recycle temperatures at about 900- 1400 F., char recycle to fresh coal weight ratios of about l5-30:1 and an oxygen supply of about .03 -.3 lb. /lb. of fresh coal. The total amount of.

. vide relatively higher phase densities of, say,

about -50 lbs. per cu. ft. The superficial gas velocity may drop from about 3-30 ft. per second in chamber 30 to about 0.1-3 ft. per second in section 25 of chamber 20.

Gaseous and vaporous carbonization products mixed with fiuidizing and fiue gases and containing small amounts of suspended solids fines are withdrawn from section 25 through a conventional gas-solids separator, such as cyclone 3| wherein most of the entrained fines are separated. The separated solids may be returned through pipe 32 to annular space 22. Gases and vapors now substantially free of entrained solids are passed through line 34 to a conventional product recovery system (not shown). Product char may be withdrawn from annular space 22 through bottom drawoif pipe 36 under the pseudo-hydrostatic pressure of the dense solids phase in 22.

The embodiment of the invention illustrated by Figure 1 permits of various medications. If desired, mechanical fiow control means such as adjustable orifices 38 may be provided to permit an additional control of char circulation from space 22 to chamber 30. Inertgases, such as steam, C02, etc. may be supplied through a number of taps 40 to annular space 22 to strip the char of valuable volatile products prior to its entry into mixing chamber 30 and thus to reduce the loss of desirable products, by combustion. This stripping gas may simultaneously aid in the fiuidization of the solids in annular space 22. The sensible heat of product solids and/or gases may be utilized to preheat process solids and/or gases in any suitable manner known per se. The system may also be readily adapted to the production of gases containing CO, such as producer gas, water gas or feed gas for the hydrocarbon synthesis by the conversion of CO with H2, by raising the temperature in chambers and 30 ,to gasification temperature and supplying adequate amounts of steam and oxidizing gas to chambers 20 and/ or 30. Other modifications will appear to those skilled in the art without deviating from the spirit of the present invention.

In the embodiment of the invention described with reference to Figure 1, the volatile process products will be diluted with fiue gases. While this may be avoided by supplying all the heat required for carbonization or gasification in the form of sensible heat of highly preheated inert gas or steam supplied through line I5, I have shown a system more suitable for this purpose in Figure 2 of the drawing, wherein like reference numerals vdesignate like elements of the systems of Figures 1 and 2.

Referring now to Figure 2, the system illustrated therein comprises processing equipment consisting essentially of processing chamber 20 and mixing chamber 30, as well as a separate heater 50, whose functions and cooperation will be explained using the conversion of coal having objectionable plastic qualities, with steam into water gas as an example. Other types of processing such as carbonization or producer gas generation may be carried out in a substantially analogous manner.

In operation. chambers 23 and 33 function sub- 6 stantially as described in connection with Figure 1. Fresh coalof, fluidizable particle sizeis supplied from feed hopper l' by feeding means, such as an aerated standpipe I, ,to thebottom portion of chamber 30 where it is intimatelymixed with'a large excess of hot ',dry" char circulated from annular space 22 to the bottom of chamber 30 substantially as described above. The upfiow of solids in chamber 30 is caused by preferably preheated steam supplied through line I! to chamber 30. Additional steam for reaction and/or fluidization may be added through lines 40 to annular space 22. The total amount of steam supplied should be sufllcient to convert a high percentage of the coal supplied, into CO and H: and to establish the desired flow conditions described above. About 0.2 to 3.0 lbs. of steam per lb. of coal fed is generally sufllcient for this purpose. The heat required to maintain chambers 20 and 30 at gasification temperatures of about 1600-2500 F. is generated and supplied as will be forthwith explained.

Char from annular space 22 is. withdrawn through a preferably aerated bottom drawofl line 38 to discharge into air line l3 which receives preferably preheated air from blower 9 through knockout drum H. A relatively dilute suspension of char in air forms in pipe 13 and this suspension is forced under the combined airpressure in line l3 and pseudo-hydrostatic pressure in pipe 33 upwardly to fluid-solids heater 50. Small amounts of a stripping gas may be introduced through tap 31 into pipe 33.

The amount of air supplied through line l3 should be sumcient to make available the oxygen required to generate heat of combustion adequate to support the gasification reaction in chambers 20 and 30. About 15 to 200 s. c. f. of air per pound of fresh coal is normally suitable to maintain a temperature in heater of about 50-300-F. higher than the temperature desired in chambers 20 and 30. This amount of air is based on a solids supply of about 30 to 300 lbs., through lines 33 and [3, per pound of fresh coal to be gasified. The air enters heater 50 through a distributing grid 52 at a linear superficial velocity of about 0.3-10 ft. per second to convert in cooperation with the fiue gases produced, the solids in combustion zone 50 into a dense fluidized mass having an upper level L50. Flue gases are withdrawn overhead from level Leo, passed through a cyclone separator 55 and vented through line 51, if desired after heat exchange with process steam. Solids separated in cyclone 55 may be returned to chamber 50 through. pipe 59. t Solid combustion residue is withdrawn downwardly from a point above grid 52 throughline Bl which may be an aerated standpipe. The flow of solids through pipe BI is controlled by slide valve 65.. Solid combustion residue from =pipe 3| enters the bottom portion of chamber 30 substantially at the temperature of heater 50 and at approximately the same rate at which solids are withdrawn through line 38 from zone 22, to supply heat required in chambers 20 and 30.

Enlarged section 25, cyclone 3|, solids return line 32 and gas recovery line 34 operate substantially as described with reference to Figure 1. Ash may be purged from pipe 32 through line 33, as desired. In addition undesired solidsaccumulation in the system may be prevented by withdrawing solids through line 35.

- The system of Figure 2 permits of similar modifications as outined with reference to Figure 1.

aaaavn lower section of chamber 30 may be so shaped as to utilize the jet action of the gas stream entering through line I! to assist in accomplishing the complete mixing of the fresh and recirculated solids and in substantially eliminating the escape of this gas stream into the lower portion of annular zone 22. This may be accomplished by giving the lower section of chamber 30 a venturitype shape as illustrated in the drawing. Carbonization may be carried out by simply lowering processing and heater temperatures accordingly, while substitution of steam by air, oxygen and/or Ca will permit producer gas generation, in a manner obvious to those skied in the art.

The invention will be further illustrated by the following specific example.

Example Operating conditions for the carbonization of Pittsburgh seam-bituminous coal containing free moisture, -35% of volatiles and having a plasticizing temperature range of about 700-800 F. and an incipient carbonization temperature of about 700 F. may be as given below when using a system of the type illustrated in Figure 1.

Fresh coal fed to carbonizer:

Gas feed rate to mixing chamber 30.

Air 5. c. f. m. 170

Height of mixing chamber 30, ft 22 Coke feed rate from annular space 22 to mixing chamber 80, lbs./hr. 30,000 Density in annular space 22, lbs./c. f. 25 Yields:

Char, weight per cent 71.6 Gas, M. M. B. t. u./hr. (net) 1.28 Tar, gala/hr. 22.4

While the foregoing description and exemplary operations have served to illustrate specific applications and results of my invention, other modifications obvious to those skilled in the art are within the scope of my invention. Only such limitations should be imposed on the invention as are indicated in the appended claims.

1. The method of carbonizing fresh subdivided carbonizable solids having a plastic temperature range, at a carbonization temperature not below said plastic range to produce volatile products, which comprises supplying said fresh solids directly to a confined open-ended passageway centrally arranged and terminating within a vessel, passing a free oxygen-containing gas upwardly through said confined passageway at a velocity sufllcient to entrain and carry upwardly. said solids. burning by said oxygen combustibles prescut in said passageway so as to supply directly to said passageway in direct heat exchange with said fresh solids substantially all the heat required to maintain in said vessel said carbonization temperature, overflowing said solids from the top of said passageway into and down through the annular space between said passageway and said vessel in the form of a fluidized solids mass having a density greater than that of the suspension in said passageway, maintaining the atmosphere within said annular space substantially inert to said solids and their carbonization products, passing solids from the bottom of said annular space into the bottom of said passageway by virtue of the pressure differential existing therebetween, said fresh solids being supplied from a source external to said vessel, maintaining the solids residence time in said passageway within the range of about 3-60 seconds but not substantially greater than that required to heat said fresh solids to said carbonization temperature in said passageway and insumcient completely to carbonize said fresh solids in said passageway, and maintaining said solids in said annular space for a time sufllcient to complete the carbonization, carbonization temperature having been attained in the upper portions of said passageway.

2. The method of claim 1 in which said solids flowing from the bottom of said annular space into the bottom of said passageway are supplied to said passageway at a rate substantially greater than that of the supply of fresh solids to said passageway.

3. The method of claim 2 in which said higher rate is a high multiple of said fresh solids feed rate.

4. The method of claim 1 in which small amounts of an inert gas are supplied to a lower portion of said annular space.

5. The method of claim 4 in which said inert gas is a stripping gas.

6. The method of claim 4 in which said inert gas is a fluidizing gas.

' 7. The method of claim 1 in which said velocity is lower in the upper portion of said passageway than in its lower portion.

8. The method of claim 1 in which said gas exerts a jet effect when entering said passageway.

' establish an apparent phase density of about 1-30 lbs. per cu. ft. in said passageway.

KARL J. NELSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,899,887 Thiele Feb. 28, 1933 2,378,342 Voorhees et al June 12, 1945 2,445,327 Keith July 20, 1948 2,462,366. Davies et al. Feb. 22, 1949 2,480,670 Peck Aug. 30, 1949 FOREIGN PATENTS Number Country Date 632,466 France -1 Oct. 10, 1927 578,711 Great Britain July 9, 1946 586,391 Great Britain Mar. 18, 1947 582,055 Great Britain Nov. 4, 1940 

1. THE METHOD OF CARBONIZING FRESH SUBDIVIDED CARBONIZABLE SOLIDS HAVING A PLASTIC TEMPERATURE RANGE, AT A CARBONIZATION TEMPERATURE NOT BELOW SAID PLASTIC RANGE TO PRODUCE VOLATILE PRODUCTS, WHICH COMPRISES SUPPLYING SAID FRESH SOLDIS DIRECTLY TO A CONFINED OPEN-ENDED PASSAGEWAY CENTRALLY ARRANGED AND TERMINATING WITHING A VESSEL, PASSING A FREE OXYGEN-CONTAINING GAS UPWARDLY THROUGH SAID CONFINED PASSAGEWAY AT A VELOCITY SUFFICIENT TO ENTRAIN AND CARRY UPWARDLY SAID SOLIDS, BURNING BY SAID OXYGEN COMBUSTIBLES PRESENT IN SAID PASSAGEWAY SO AS TO SUPPLY DIRECTLY TO SAID PASSAGEWAY IN DIRECT HEAT EXCHANGE WITH SAID FRESH SOLIDS SUBSTANTIALLY ALL THE HEAT REQUIRED TO MAINTAIN IN SAID VESSEL SAID CARBONIZATION TEMPERATURE, OVERFLOWING SAID SOLIDS FROM THE TOP OF SAID PASSAGEWAY INTO AND DOWN THROUGH THE ANNULAR SPACE BETWEEN SAID PASSAGEWAY AND SAID VESSEL IN THE FORM OF A FLUIDIZED SOLIDS MASS HAVING A DENSITY GREATER THAN THAT OF THE SUSPENSION IN SAID PASSAGEWAY, MAINTAINING THE ATMOSPHERE WITHIN SAID ANNULAR SPACE SUBSTANTIALLY INERT TO SAID SOLIDS AND THEIR CARBONIZATON PRODUCTS, PASSING SOLIDS FROM THE BOTTOM OF SAID ANNULAR SPACE INTO THE BOTTOM OF SAID PASSAGEWAY BY VIRTUE OF THE PRESSURE DIFFERENTIAL EXISTING THEREBETWEEN, SAID FRESH SOLIDS BEING SUPPLIED FROM A SOURCE EXTERNAL TO SAID VESSEL, MAINTAINING THE SOLIDS RESIDENCE TIME IN SAID PASSGEWAY WITHIN THE RANGE OF ABOUT 3-60 SECONDS BUT NOT SUBSTANTIALLY GREATER THAN THAT REQUIRED TO HEAT SAID FRESH SOLIDS TO SAID CARBONIZATION TEMPERATURE IN SAID PASSAGEWAY AND INSUFFICIENT COMPLETELY TO CARBONIZE SAID FRESH SOLIDS IN SAID PASSAGEWAY, AND MAINTAINING SAID SOLIDS IN SAID ANNULAR SPACE FOR A TIME SUFFICIENT TO COMPLETE THE CARBONIZATION, CARBONIZATION TEMPERATURE HAVING BEEN ATTAINED IN THE UPPER PORTIONS OF SAID PASSAGEWAY. 